The present invention generally relates to a computer terminal CRT display apparatus, and more particularly, to a power supply apparatus therefor.
Generally, the CRT power supply apparatus employs a switching power supply circuit (or switching regulator) which converts a rectified voltage into a high frequency AC voltage by carrying out a switching operation, and which thereafter rectifies the high frequency AC voltage to obtain a direct current. In order to prevent the noises caused by the switching operation of the power supply from interrupting the horizontal synchronization, the switching is conventionally adapted to be synchronized by using the horizontal output pulse as a trigger.
A low-tension output power supply is sometimes employed, except for the horizontal output circuit, as the power supply. The switching of such a low-tension output power supply is self-operated in that triggering is not applied by the horizontal output pulse. When the horizontal output circuit or the power supply thereof malfunctions, the horizontal output pulse is not generated. If the low-tension output power supply is triggered with the pulse, the power supply also does not operate properly, so that the entire apparatus becomes inoperative. Thus, identifying the location of the breakdown is difficult. Therefore, the switching noises caused by the low-tension output power supply are not synchronized with the horizontal output circuit. If it should malfunction, only a condition where the low-tension output power supply has not broken down is adapted to be judged at least.
Although the conventional television is required to be horizontally synchronized only in the high-tension output power supply, the high-precision CRT display apparatus recently employed for computer usage entails a problem in that noises caused by the low-tension voltage output power supply are not synchronized with the horizontal output circuit. As such, noises of the display may be conspicuous due to the disturbances of the operations of the horizontal oscillating circuit and the horizontal output circuit.